The shaft of a conventional golf club as shown in FIG. 1 will always be bent in a so-called primary mode in mechanics when the golf club is being swung. The primary mode is shown in FIG. 2 where the end 2 is the butt end of the shaft in the grip portion and the other end 3 is a free end where a head is attached. The inertia force 4 would be acting when the club is being swung. From point 5 to 6, a simple harmonic half-wave curve is formed by the axis of the bent shaft. Such bent shape is called a primary mode. The bent shaft should recover its straightness at the end of the swing and the speed of the head at the instant the head hitting the ball depends on the speed of recovery of the curved shape back to its undeformed state. The time required to become straight is called frequency. The invention is to install a structural member in the interior space of the shaft which will interact with the shaft when the shaft bends so as to alter said primary mode of the bent shaft into a higher frequency mode so that the recovery of the bent shape of the golf club shaft to become straight again could be faster, and consequently the speed of the head when it hits the ball is greater than the conventional shaft bent in the primary mode.